Modes

Secrets

Acquire Guilty Gear Mode - Alternate Method

With Testament and Dizzy already unlocked, set the difficulty to anything above Beginner, and the timer to 60. Now go through Arcade mode without losing a single match, or continuing. Guilty Gear Mode will become available.

Unlocking Costumes

You can unlock extra costumes when you play Survival Mode, when you beat or die from a character that it was your first time seeing that costume. After that, that costume will be accessible by pressing and holding in a button when selecting that character.

Note: This doesn't mean all the other character's costumes will be unlocked, you'll have to play Survival Mode until you see a certain character with a different costume.